The invention relates to an orthopaedic insole with a top cover and a bottom cover, which covers enclose a support core, the top cover and the bottom cover projecting beyond the support core via an edge area and being connected to each other in the edge area.
Such an insole is known from German Patent Specification 4,437,282. According to that document, the known insole is produced by means of covers, designated as cutouts, being pre-heated together with a shaped part which forms the support core, and this is done preferably without adhesive, after which these parts are joined together. The bottom cover is therefore preferably provided with adhesive. No other method of connecting the two covers is mentioned in the document.
The object of the invention is to design the insole in such a way that it can be produced by a relatively simplified method and obtains a special internal stability. According to the invention, this is achieved by the fact that both the top cover and bottom cover and also the support core are made of a thermoplastic material, the melting points of the three component parts of the insole, namely support core, top cover, and bottom cover, having approximately the same value, and these component parts being permanently connected to one another by pressing and shaping, with melting-on of the contiguous surfaces. In the insole according to the invention, there is a fixed connection between the top cover and the support core and between the bottom cover and the support core and also between the edge areas of the top cover and bottom cover projecting beyond the support core, which connection is achieved by a sort of welding-together of the contiguous surfaces, and, in addition, the support core obtains its final therapeutically requisite shape by means of the pressing and shaping, so that the insole is thus formed in a single method step by permanent connection of its three component parts and this shaping. The insole is therefore the result of a single step in which the unworked component parts of the insole, superposed loosely in a press mould, are pressed together, the melting of the contiguous surfaces at the same time bringing about the permanent inner connection of the component parts, and the associated shaping bringing about the final configuration of the insole. A crucial factor in this is that all the component parts of the insole are made of a thermoplastic material and the melting points of the three component parts have approximately the same value, so that the procedure outlined above can bring about the connection of all the component parts in a single step, these component parts then jointly forming the insole, with adaptation to the therapeutic conditions. The top cover is advantageously provided with a skin-compatible covering, for which leather, imitation leather, plastic or the like can be used.
To form the support core, it is possible to use a homogeneous material, e.g. a plastic sheet flattened at its edges. However, it is also possible and particularly advantageous to form the support core using two superposed sheets which each entail a loose running material. Fine plastic granules can be used here which flow upon being heated and form a sheet when cooled. The plastic granules are poured into a mould in which they are made to flow by heating and are limited in terms of their contour by the mould. Thus, sheets of the desired thickness and contour are produced in a known manner, and they are then placed one upon the other, the lower sheet having a shorter longitudinal extent than the upper sheet in order to form the support core. The lower sheet thus essentially forms the support part of the insole which is then given the desired shape for the required therapy by means of shaping and pressing.
To give the insole a high degree of stability, while preserving its bending strength, one of the two covers or both the top cover and bottom cover are made from a two-layer material, in which the inner layer (facing the support core) consists of a woven netting formed by a thermoplastic fibre. The outer layer consists of a thermoplastic film, the melting point of the woven netting and of the plastic film corresponding to that of the three component parts, that is to say the top cover, support core and bottom cover. By using the woven netting, the insole acquires quite considerable strength in its longitudinal extent without thereby losing bending strength, with the result that the insole can, as before, readily adapt to the bending of the shoe as the user is walking. The woven netting ensures that even the support core, which normally forms a cavity directed away from the foot, is given a high degree of elasticity, since the loading of the insole by the foot is in this case taken up not only by the support core alone, but also by the woven netting.